feat: add stats breakdown view

[OneNoted]

Summary

Adds a ghfetch breakdown <username> command that explains which repositories contribute to language totals and estimated LoC. The new view supports language-first and repo-first grouping, JSON output, filtering by language or repository, output limits, and fork exclusion.

Also makes fork exclusion easier to discover across repository-total views by exposing --ignore-forks as an alias for --no-forks, and applies fork filtering to organization language and repository totals.

Validation

• cargo fmt --check
• cargo test
• cargo clippy --all-targets --all-features -- -D warnings
• cargo run --quiet -- user --help
• cargo run --quiet -- org --help
• cargo run --quiet -- breakdown --help

[OneNoted]

Superseded by #5, which is based directly on main and contains only the breakdown feature changes.